Quantum dot structure, quantum dot light-emitting device and preparation method of quantum dot light-emitting layer

Abstract

The invention relates to the technical field of display, and particularly discloses a quantum dot structure which comprises a quantum dot body, a first ligand and a second ligand, the first ligand is connected to any binding site on the surface of the quantum dot body through a first coordinate bond, and the second ligand is connected to any binding site on the surface of the quantum dot body through a second coordinate bond. The second ligand is connected to a binding site on the surface of one side of the quantum dot body through a second coordinate bond, the binding force of the second coordinate bond and the quantum dot body is larger than that of the first coordinate bond and the quantum dot body, and the HOMO / LUMO energy level of the second ligand is limited within a special range. According to the quantum dot light-emitting device using the quantum dot structure, the electron mobility of the inorganic electron transport layer can be reduced, and the carrier balance of the device can be adjusted; moreover, leakage current caused by direct lap joint of the electron transport layer and the hole transport layer can be avoided, so that the efficiency and the service life of the light-emitting device are improved.

Description

Technical Field

[0001] The present invention relates to the field of display technology, and in particular to a quantum dot structure, a quantum dot light-emitting device including the quantum dot structure, and a method for preparing a quantum dot light-emitting layer including the quantum dot structure. Background Art

[0002] Quantum dot light-emitting devices have advantages such as high color gamut, potential long life, good viewing angle and low cost. They are a very promising future display technology. However, there are still some problems that need to be solved urgently. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and provide a quantum dot structure, a quantum dot light-emitting device including the quantum dot structure, and a method for preparing a quantum dot light-emitting layer including the quantum dot structure. The quantum dot structure includes a quantum dot body, a first ligand, and a second ligand. The first ligand is connected to any binding site on the surface of the quantum dot body through a first coordination bond, and the second ligand is connected to a binding site on the side surface of the quantum dot body through a second coordination bond. The binding force of the second coordination bond with the quantum dot body is greater than the binding force of the first coordination bond with the quantum dot body, and the HOMO / LUMO energy level of the second ligand is limited to a specific range. A quantum dot light-emitting device using this quantum dot structure can, on the one hand, reduce the electron mobility of the inorganic electron transport layer and adjust the carrier balance of the device; on the other hand, it can avoid leakage current caused by direct overlap between the electron transport layer and the hole transport layer, thereby improving the efficiency and service life of the light-emitting device.

[0004] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a quantum dot structure, including a quantum dot body, a first ligand and a second ligand, wherein the first ligand is connected to any binding site on the surface of the quantum dot body through a first coordination bond, and the second ligand is connected to a binding site on one side surface of the quantum dot body through a second coordination bond, the binding force between the second coordination bond and the quantum dot body is greater than the binding force between the first coordination bond and the quantum dot body, the HOMO energy level of the second ligand is less than -6eV, and the LUMO energy level is -3.5eV to -1eV.

[0005] A second aspect of the present invention provides a quantum dot light-emitting device, comprising a substrate, a first electrode, a first functional layer, a quantum dot light-emitting layer, a second ligand layer, a second functional layer, and a second electrode stacked in sequence on one side of the substrate;

[0006] In which, the first electrode includes an anode, the first functional layer includes a hole injection layer and a hole transport layer stacked in sequence, the second electrode includes a cathode, the second ligand layer includes the second ligand, the second functional layer includes an electron transport layer, and the quantum dot light-emitting layer includes the quantum dot structure provided in the first aspect of the present invention.

[0007] The third aspect of the present invention provides a method for preparing a quantum dot light-emitting layer comprising the quantum dot structure provided in the first aspect of the present invention, or a method for preparing the quantum dot light-emitting layer in the quantum dot light-emitting device provided in the second aspect of the present invention, comprising:

[0008] (1) treating the quantum dot body with the first ligand to obtain the quantum dot structure with the first ligand coordinated to any binding site on the surface;

[0009] (2) forming the material obtained in step (1) into a thin film to form a quantum dot light-emitting layer in which any binding site on the surface is coordinated with the first ligand;

[0010] (3) Using a second ligand treating agent containing the second ligand to treat the surface arbitrary binding sites obtained in step (2) to coordinate the quantum dot light-emitting layer of the first ligand away from the surface of the substrate, to form the quantum dot light-emitting layer and the second ligand layer.

[0011] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0012] The second ligand of the present invention is bound to the binding site on one side of the quantum dot body based on the first ligand binding site by undergoing ligand exchange with the first ligand. On the one hand, the diameter of the quantum dots can be increased so that the second ligand fills the pores between the quantum dots, avoiding direct overlap between the electron transport layer and the hole transport layer to generate leakage current; on the other hand, since the HOMO energy level of the second ligand is deeper, holes will not be injected into the second ligand, so it can also avoid indirect overlap between the electron transport layer and the hole transport layer to generate leakage current, thereby improving the luminous efficiency and service life of the quantum dot light-emitting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Shown is a schematic diagram of the quantum dot structure of the present invention;

[0014] Figure 2 Shown is a SEM cross-sectional view of a commonly used quantum dot light-emitting layer thin film structure;

[0015] Figure 3 The structure of the quantum dot light emitting device of the present invention is shown as follows Figure 1 ;

[0016] Figure 4The structure of the quantum dot light emitting device of the present invention is shown as follows Figure 2 ;

[0017] Figure 5 The figure shows a schematic diagram of the preparation process of the quantum dot light-emitting layer of the present invention;

[0018] Figure 6 Shown is an energy level diagram of the quantum dot light-emitting device structure of the present invention. DETAILED DESCRIPTION

[0019] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0020] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by persons of ordinary skill in the field to which this disclosure belongs. The words "first", "second" and similar terms used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0021] The first aspect of the present invention provides a quantum dot structure, including a quantum dot body, a first ligand and a second ligand, the first ligand is connected to any binding site on the surface of the quantum dot body through a first coordination bond, and the second ligand is connected to a binding site on one side surface of the quantum dot body through a second coordination bond, the binding force between the second coordination bond and the quantum dot body is greater than the binding force between the first coordination bond and the quantum dot body, the HOMO energy level of the second ligand is less than -6eV, and the LUMO energy level is -3.5eV to -1eV.

[0022] In the present invention, the quantum dot body can be specifically selected from at least one of CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe of the II-VI group or GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, AlP, AlSb of the III-V group.

[0023] In the present invention, the binding force between the second coordination bond and the quantum dot body is greater than the binding force between the first coordination bond and the quantum dot body. Since the binding ability between the second coordination bond and the quantum dot body is stronger, if the second ligand is used to treat the surface of the quantum dot body covered with the first ligand, the second ligand will exchange ligands with the first ligand partially covered on the surface of the quantum dot body (such as Figure 1 1) or 2) in the figure), thereby replacing the original ligand and remaining on the surface of the quantum dot body.

[0024] Furthermore, the first ligand is connected to any binding site of the quantum dot body through a first coordination bond, and the second ligand that has undergone ligand exchange with the first ligand is connected to a binding site on one side surface of the quantum dot body through a second coordination bond. It should be noted that the quantum dot body is generally spherical or quasi-spherical, and therefore, the active sites on one side surface of the spherical or quasi-spherical quantum dot body refer to the active sites of half of the entire spherical surface. Specifically, the active sites on one side surface of the quantum dot body may include upper part active sites and side part active sites; wherein, the "upper part" refers to the active sites on the part of the surface of one side surface of the quantum dot structure away from the substrate of the OLED light-emitting device when the quantum dot structure is flattened to form a quantum dot light-emitting layer and is coated in an OLED light-emitting device, such as Figure 1 As shown in Figure 1); the "lateral portion" refers to when the quantum dot light-emitting layer film formed by the quantum dot structure is not dense enough and there is a gap between two adjacent quantum dot structures, then the active site on the surface of one side of the quantum dot structure that is closer to the other quantum dot structures is called the lateral portion active site, such as Figure 1 As shown in Figure 2), the second ligand can be present at both the upper active site and the side active site on one side of the quantum dot body. The second ligand connected to the binding site on the side of one side of the quantum dot body through a second coordination bond can increase the diameter of the quantum dot body due to the special nature of its binding position, thereby filling the pores formed by the uneven film formation of the quantum dot structure, avoiding direct overlap between the electron transport layer and the hole transport layer, improving the problem of internal leakage current of the device, and thus improving the efficiency and life of the device.

[0025] Furthermore, the HOMO energy level of the second ligand is less than -6eV, and its LUMO energy level is in the range of -3.5eV to -1eV. By further setting the HOMO energy level and LUMO energy level of the second ligand within a specific range, leakage current in the device can be further effectively avoided. For example, when the HOMO energy level of the second ligand is less than -6eV, the HOMO energy level of the second ligand is less than the HOMO energy level of the quantum dot light-emitting layer when only the first ligand is bound. The quantum dot structure formed by simultaneously coordinating the first ligand and the second ligand can effectively prevent the hole transport layer from injecting holes into the second ligand. When the LUMO energy level of the second ligand is between -3.5eV and -1eV, the LUMO energy level of the second ligand is higher than the LUMO energy level of the quantum dot light-emitting layer when only the first ligand is bound, but lower than the LUMO energy level of the hole transport layer material. The quantum dot structure formed by simultaneously coordinating the first ligand and the second ligand can enable electrons to be effectively injected into the quantum dot light-emitting layer without being injected into the hole transport layer and causing leakage current.

[0026] In a specific embodiment, the HOMO energy level of the second ligand can be -5.5 eV, -5 eV, -4.5 eV, -4 eV, -3.5 eV, -3 eV, -3.5 eV, -2 eV, or a range consisting of any two values.

[0027] In a specific embodiment, the LUMO energy level of the second ligand can be -3.5 eV, -3 eV, -2.5 eV, -2 eV, -1.5 eV, -1 eV, or a range consisting of any two values.

[0028] With the development of quantum dot light-emitting devices, there is a gradual trend to spread spherical quantum dots in the device to form a thin film layer, such as Figure 2As shown in the figure, some quantum dot light-emitting layers may only have about two layers of quantum dots after film formation (QD layer, between the ZnMgO layer and the TFB layer, wherein the ZnMgO layer is the electron transport layer in the quantum dot light-emitting device, and the TFB layer is the hole transport layer in the quantum dot light-emitting device). Therefore, it is easy for some areas to be unevenly formed, and some areas will form gaps. During the preparation and actual application process, it is easy to cause the electron transport layer and the hole transport layer to directly overlap, resulting in leakage current. Therefore, based on the above problems, the inventors of the present invention found that on the basis of the surface coordination with the first ligand, the surface on the side away from the substrate of the light-emitting device is treated with a treating agent containing a second ligand, so that the second ligand can be coordinated to one side of the binding site on the surface of the quantum dot body. Due to the special properties of the second ligand, on the one hand, the HOMO energy level of the second ligand is deeper, which can avoid hole injection and play a role in reducing leakage current. On the other hand, if the film formation area of ​​some quantum dot light-emitting layers is uneven and there are gaps, the second ligand is connected to the binding site on the side surface of the quantum dot body through a second coordination bond, which can increase the diameter of the quantum dot body and fill the gaps, thereby avoiding direct overlap of the electron transport layer and the hole transport layer, thereby causing leakage current.

[0029] Therefore, the above-mentioned solution of the present invention can achieve better effects than the prior art. In order to further improve the effects, one or more of the following solutions can be further defined.

[0030] In one embodiment, the electron mobility of the second ligand is 10 -5 cm 2 / V·s~10 -3 cm 2 / V·s. In one embodiment, the electron mobility of the second ligand can be 10 -5 cm 2 / V·s、10 -4 cm 2 / V·s、10 -3 cm 2 / V·s or a range consisting of any two values. It can be understood that by setting the electron mobility of the second ligand within a specific range, the electron mobility of the second ligand can be made smaller than the electron mobility of the inorganic substances (such as ZnO, ZnMgO, etc.) commonly used in the electron transport layer, thereby reducing the electron mobility of the quantum dot structure treated with the second ligand, avoiding the situation of more electrons and fewer holes, and solving the problem of carrier imbalance inside the quantum dot light-emitting device, thereby further improving the luminous efficiency and life of the quantum dot light-emitting device.

[0031] In one embodiment, the first ligand includes a first coordinating group that provides a first coordination bond, and the second ligand includes a second coordinating group that provides a second coordination bond. The first coordinating group of the first ligand forms a first coordination bond after bonding with the quantum dot body, and the second coordinating group of the second ligand forms a second coordination bond after bonding with the quantum dot body.

[0032] In one embodiment, the first ligand group includes a combination of one or more of a carboxyl group, an amino group, a polyamino group, or a phosphorus oxygen group.

[0033] In one embodiment, the second ligand group includes a thiol group, a polythiol group, or a combination of one or more of the group consisting of thiol and polythiol.

[0034] The second coordination group has a stronger binding ability with the quantum dot body. After the surface of the quantum dot body is treated with a treating agent containing the second ligand, some of the first ligand will exchange ligands with the second ligand, so that the second ligand will remain on the surface of the quantum dot body, thereby enabling it to further play a role in balancing carriers and preventing leakage current.

[0035] In the present invention, the first ligand comprises a combination of one or more of a linear fatty acid ligand, a branched fatty acid ligand, a fatty amine ligand, and a phospho-oxygen ligand. The linear fatty acid ligand or the branched fatty acid ligand comprises a carboxyl group, the fatty amine ligand comprises an amino group or a polyamino group, and the phospho-oxygen ligand comprises a phospho-oxy group. In one specific embodiment, the linear fatty acid ligand may be oleic acid. In another specific embodiment, the fatty amine ligand is oleylamine.

[0036] In the present invention, the second ligand includes a non-coordinating group, which is connected to the quantum dot body via the second coordinating group. The non-coordinating group of the second ligand plays a role in regulating the HOMO / LUMO energy levels of the second ligand.

[0037] In a specific embodiment, the non-coordinating group includes a combination of one or more of a carbazole group, a phenyl group, an aniline group, a phenyl ether group, a phenylthio group, a thienyl group, a benzothienyl group, and a benzofuranyl group; further, since the carbazole group has a lower electron mobility and a higher LUMO energy level, the non-coordinating group is further preferably a carbazole group.

[0038] In the present invention, the second ligand has a structural formula shown in the following formula (I) or formula (II), specifically as follows:

[0039]

[0040] Wherein, R1 is the second coordination group, and R1 is selected from: -(CH2) nSH, n is an integer of 2-18; R2 and R3 are each independently selected from at least one of hydrogen, hydroxyl, C1-C36 alkyl which may be substituted or unsubstituted, cyano which may be substituted or unsubstituted, and C1-C36 phenyl which may be substituted or unsubstituted, and the substituent is F, Cl, Br, or I; R4, R5, R6, R7, and R8 are each independently selected from at least one of F, Cl, Br, I, CN, and OH.

[0041] In one embodiment, R1 is selected from: -(CH2) n SH, n is an integer of 2-12; R2 and R3 are each independently selected from at least one of hydrogen, hydroxyl, C1-C12 alkyl which may be substituted or unsubstituted, C1-C12 cyano which may be substituted or unsubstituted, and C1-C12 phenyl which may be substituted or unsubstituted, and the substituent is F; R4, R5, R6, R7, and R8 are each independently selected from F.

[0042] In one embodiment, the structural formula of the second ligand includes one or more combinations of the following:

[0043]

[0044]

[0045] The second aspect of the present invention provides a quantum dot light emitting device, such as Figure 3 As shown, it includes a substrate, a first electrode, a first functional layer, a quantum dot light-emitting layer, a second ligand layer, a second functional layer and a second electrode stacked in sequence on one side of the substrate;

[0046] In which, the first electrode includes an anode, the first functional layer includes a hole injection layer and a hole transport layer stacked in sequence, the second electrode includes a cathode, the second ligand layer includes the second ligand, the second functional layer includes an electron transport layer, and the quantum dot light-emitting layer includes the quantum dot structure provided in the first aspect of the present invention.

[0047] Specifically, such as Figure 4As shown, the second ligand coverage on the surface of the quantum dot light-emitting layer away from the substrate is greater than the second ligand coverage on the surface close to the substrate. The reason for this difference in second ligand coverage is that after the quantum dot light-emitting layer thin film is formed, the surface is treated with a treatment agent containing the second ligand. Therefore, the second ligand coverage on the surface close to the substrate of the quantum dot light-emitting layer is lower, while the second ligand coverage on the surface away from the substrate of the quantum dot light-emitting layer is higher. At this time, a portion of the second ligand will bind to the surface of the quantum dot light-emitting layer away from the substrate. In other words, a portion of the second ligand will bind to the binding sites on the surface of the quantum dot body in the quantum dot light-emitting layer away from the substrate. The excess second ligand will form a second ligand coverage layer between the electron transport layer and the quantum dot light-emitting layer, namely the second ligand layer. This adjustment can not only adjust the carrier balance, but also avoid leakage current caused by direct or indirect overlap between the electron transport layer and the hole transport layer, thereby improving the luminous efficiency and service life of the device.

[0048] In one embodiment, the HOMO energy level of the second ligand is less than -6 eV, and the LUMO energy level is between -3.5 eV and -1 eV.

[0049] In one embodiment, the electron mobility of the second ligand is 10-5 cm 2 / V·s~10-3cm 2 / V·s.

[0050] In one embodiment, the second ligand has the following structural formula (I) or (II):

[0051]

[0052] Wherein, R1 is the second coordination group, and R1 is selected from: -(CH2) n SH, n is any integer from 2 to 18;

[0053] R2 and R3 are each independently selected from at least one of hydrogen, hydroxyl, C1-C36 alkyl which may be substituted or unsubstituted, C1-C36 cyano which may be substituted or unsubstituted, and C1-C36 phenyl which may be substituted or unsubstituted, wherein the substituent is F, Cl, Br, or I;

[0054] R4, R5, R6, R7, and R8 are each independently selected from at least one of F, Cl, Br, I, CN, and OH.

[0055] In one embodiment, the structural formula of the second ligand includes one or more combinations of the following:

[0056]

[0057]

[0058] The third aspect of the present invention provides a method for preparing a quantum dot light-emitting layer comprising the quantum dot structure provided by the first aspect of the present invention, or a method for preparing the quantum dot light-emitting layer in the quantum dot light-emitting device provided by the second aspect of the present invention, such as Figure 5 As shown, including:

[0059] (1) treating the quantum dot body with the first ligand to obtain the quantum dot structure with the first ligand coordinated to any binding site on the surface;

[0060] (2) forming the material obtained in step (1) into a thin film to form a quantum dot light-emitting layer in which any binding site on the surface is coordinated with the first ligand;

[0061] (3) Using a second ligand treating agent containing the second ligand to treat the surface arbitrary binding sites obtained in step (2) to coordinate the quantum dot light-emitting layer of the first ligand away from the surface of the substrate, to form the quantum dot light-emitting layer and the second ligand layer.

[0062] Specifically, step (1) also includes the preparation of quantum dot bodies.

[0063] In step (1), the preparation method of the quantum dot structure with the first ligand coordinated on the surface is as follows: a certain amount of quantum dot body pre-oxide, a first ligand treatment agent and a suitable solvent are added to a three-necked flask, and heated to 250-280°C under a nitrogen atmosphere. When the solution becomes clear, the temperature is lowered to 110-130°C and maintained for 0.5-1 hour. After removing the excess solvent, the system is heated to 250-290°C, and at the same time, a certain amount of a pre-suspension of another element of the quantum dot body (for example: a suspension of ODE-Se) is quickly added, and the heating is maintained at a temperature of 250-280°C for 1-5 minutes to obtain a quantum dot structure with the first ligand coordinated on the surface.

[0064] In step (2), the quantum dot structure obtained in step (1) can be made into a thin film by spin coating at a rotation speed of 2500-3500 rpm.

[0065] In step (3), a second ligand treating agent containing a second ligand is used to coat the surface of the quantum dot light-emitting layer formed by the thin film of the quantum dot structure prepared in step (2) and coordinated with the first ligand at any binding site on the surface, which is away from the substrate. The second ligand in the second ligand treating agent will exchange ligands with the first ligand on the upper surface of the thin film of the quantum dot structure and combine with the quantum dot body. Finally, the excess second ligand treating agent is removed by solvent development.

[0066] In order to further improve the leakage current problem of the quantum dot light-emitting layer, a second ligand treatment agent with a HOMO energy level lower than the HOMO energy level of the quantum dot light-emitting layer can be used to treat the quantum dot light-emitting layer (QD) with the first ligand coordinated to any binding site on the surface.

[0067] Furthermore, the LUMO energy level of the second ligand treatment agent should also be higher than the LUMO energy level of the quantum dot light-emitting layer (QD) coordinated with the first ligand at any binding site on the surface, and lower than the LUMO energy level of the hole transport layer (HTL). Specifically, its energy level diagram can be as follows: Figure 6 shown.

[0068] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0069] Example A-1

[0070] This embodiment uses the second ligand of the structure shown in (I-4) to form a quantum dot structure, specifically according to the following steps:

[0071] (1) Preparation of the first ligand quantum dot structure:

[0072] A three-necked flask was charged with 0.642 g of CdO, 4.75 mL of oleic acid, and 25 mL of octadecene. The mixture was heated to 260°C under a nitrogen atmosphere. After the solution became clear, the temperature was lowered to 120°C and maintained for 0.5 hours to remove excess water. The system was then heated to 270°C while a 2 mM / mL suspension of ODE-Se was rapidly added. The temperature was maintained at 260°C for 105 seconds to obtain CdSe quantum dots containing oleic acid ligands.

[0073] (2) Preparation of quantum dot light-emitting layer thin film;

[0074] The obtained CdSe quantum dots containing oleic acid ligands were prepared into a 15 mg / mL n-octane solution, and were spin-coated at a rotation speed of 3000 rpm to form a film, and annealed at 100° C. for 30 min.

[0075] (3) Preparation of the first ligand / second ligand quantum dot structure:

[0076] Dissolve the second ligand compound represented by the structural formula I-4 in a toluene solution to prepare a 50 mg / mL solution. Add the toluene solution containing the second ligand compound represented by I-4 dropwise onto the oleic acid ligand-containing CdSe quantum dot film obtained in step (2). After standing for 5 seconds, spin coat at 3000 rpm / min and anneal at 100°C for 10 minutes to obtain a CdSe quantum dot light-emitting layer comprising the first ligand and the second ligand.

[0077] Example A-2

[0078] This embodiment uses the second ligand of the structure shown in (I-5) to form a quantum dot structure, specifically according to the following steps:

[0079] (1) Preparation of the first ligand quantum dot structure:

[0080] A three-necked flask was charged with 0.543 g of CdO, 5.25 mL of oleic acid, and 25 mL of octadecene. The mixture was heated to 260°C under a nitrogen atmosphere. After the solution became clear, the temperature was lowered to 120°C and maintained for 0.5 hours to remove excess water. The system was then heated to 270°C while a 3 mM / mL suspension of ODE-Se was rapidly added. The temperature was maintained at 260°C for 200 seconds to obtain CdSe quantum dots containing oleic acid ligands.

[0081] (2) Preparation of quantum dot light-emitting layer thin film;

[0082] The obtained CdSe quantum dots containing oleic acid ligands were prepared into a 15 mg / mL n-octane solution, and were spin-coated at a rotation speed of 3000 rpm to form a film, and annealed at 100° C. for 30 min.

[0083] (3) Preparation of the first ligand / second ligand quantum dot structure:

[0084] Dissolve the second ligand compound represented by the structural formula I-5 in a toluene solution to prepare a 50 mg / mL solution. Add the toluene solution containing the second ligand compound represented by I-5 dropwise onto the oleic acid ligand-containing CdSe quantum dot film obtained in step (2). After standing for 5 seconds, spin coat at 3000 rpm / min and anneal at 100°C for 10 minutes to obtain a CdSe quantum dot light-emitting layer comprising the first ligand and the second ligand.

[0085] Example A-3

[0086] This embodiment uses the second ligand of the structure shown in (II-1) to form a quantum dot structure, specifically according to the following steps:

[0087] (1) Preparation of the first ligand quantum dot structure:

[0088] A three-necked flask was charged with 0.456 g of CdO, 4.25 mL of oleic acid, and 25 mL of octadecene. The mixture was heated to 250°C under a nitrogen atmosphere. After the solution became clear, the temperature was lowered to 120°C and maintained for 0.5 hours to remove excess water. The system was then heated to 270°C while a 2.5 mM / mL suspension of ODE-Se was rapidly added. The temperature was maintained at 270°C for 150 seconds to obtain CdSe quantum dots containing oleic acid ligands.

[0089] (2) Preparation of quantum dot light-emitting layer thin film;

[0090] The obtained CdSe quantum dots containing oleic acid ligands were prepared into a 15 mg / mL n-octane solution, and were spin-coated at a rotation speed of 3000 rpm to form a film, and annealed at 100° C. for 30 min.

[0091] (3) Preparation of the first ligand / second ligand quantum dot structure:

[0092] Dissolve the second ligand compound represented by the structural formula II-1 in a toluene solution to prepare a 50 mg / mL solution. Add the toluene solution containing the second ligand compound represented by II-1 dropwise onto the oleic acid ligand-containing CdSe quantum dot film obtained in step (2). After standing for 5 seconds, spin coat at 3000 rpm / min and anneal at 100°C for 10 minutes to obtain a CdSe quantum dot light-emitting layer comprising the first ligand and the second ligand.

[0093] Example A-4 group

[0094] Example A-4 was carried out in accordance with Example 1, except that the quantum dot bodies were changed, as shown below:

[0095] In Example A-4a, the quantum dots containing the first ligand obtained in step (1) are CdS quantum dots containing oleic acid ligands;

[0096] In Example A-4b, the quantum dots containing the first ligand obtained in step (1) are CdTe quantum dots containing oleic acid ligands;

[0097] In Example A-4c, the quantum dots containing the first ligand obtained in step (1) are InP quantum dots containing oleic acid ligands.

[0098] Example A-5 group

[0099] Example A-5 was carried out in accordance with Example 1, except that the specific structure of the second ligand was changed, as shown below:

[0100] In Example A-5a, the second ligand is a compound having the structural formula (I-1);

[0101] In Example A-5b, the second ligand is a compound having the structural formula (I-2);

[0102] In Example A-5c, the second ligand is a compound having the structural formula (I-3);

[0103] In Example A-5d, the second ligand is a compound having the structural formula shown in formula (I-7).

[0104] Example B-1 to B-5 groups

[0105] According to the preparation steps of the quantum dot light-emitting layer of the above-mentioned groups A-1 to A-5 of Examples, the above-mentioned quantum dot light-emitting layer was formed in quantum dot light-emitting devices with the same structure and composition in other layers. The specific structure of the quantum dot light-emitting device is as follows: substrate (Si) / anode (ITO) / hole injection layer (PEDOT:PSS) / hole transport layer (TPD) / quantum dot light-emitting layer / electron transport layer (ZnO) / cathode (Al).

[0106] Comparative Example B-1

[0107] Comparative Example B-1 was carried out with reference to Example B-1, except that, during the preparation of the quantum dot light-emitting layer, the quantum dot light-emitting layer film obtained in step (2) was not treated with a treating agent containing the second ligand.

[0108] Comparative Example B-2

[0109] Comparative Example B-2 is carried out with reference to Example B-1, except that in step (3) of the preparation process of the quantum dot light-emitting layer, a treating agent containing a second ligand is not used, and a treating agent containing other ligands with a HOMO energy level greater than or equal to -6 eV is selected.

[0110] The device performance of the quantum dot light-emitting devices prepared in the above-mentioned Examples B-1 to B-5 and Comparative Examples B-1 to B-2 was tested and recorded in Table 1, such as: voltage @ 6000 nit (unit: V), EQE efficiency (%) and device life T95 @ 1000 nit (unit: h).

[0111] Table 1

[0112] Group Voltage@6000nit EQE efficiency Lifespan T95@1000nit Example B-1 3.0V 23％ 9864h Example B-2 3.1V 22.5％ 9543h Example B-3 3.2V 22％ 9674h Example B-4a 3.3V 18％ 8432h Example B-4b 3.2V 19％ 8851h Example B-4c 3.0V 20％ 8558h Example B-5a 3.3V 18％ 4432h Example B-5b 3.8V 15％ 4851h Example B-5c 3.5V 12％ 4387h Example B-5d 3.4V 15％ 2073h Comparative Example B-1 4.0V 7％ 894h Comparative Example B-2 3.9V 11％ 995h

[0113] From the analysis in Table 1, it can be seen that compared with Comparative Example B-1 and Comparative Example B-2, the EQE efficiency and lifespan of Examples B-1 to B-5 groups are significantly increased, indicating that the film formation quality of the quantum dot light-emitting layer treated with the treating agent containing the second ligand is better, and the electron transport layer and the hole transport layer will not be directly overlapped to generate leakage current due to uneven film formation in some areas; moreover, since the HOMO energy level of the second ligand is deeper, holes will not be injected into the second ligand, and therefore the indirect overlap of the electron transport layer and the hole transport layer to generate leakage current can also be avoided, thereby further improving the luminous efficiency and service life of the quantum dot light-emitting device.

[0114] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A quantum dot structure, characterized in that It includes a quantum dot body, a first ligand and a second ligand, wherein the first ligand is connected to any binding site on the surface of the quantum dot body through a first coordination bond, and the second ligand is connected to a binding site on one side surface of the quantum dot body through a second coordination bond, the binding force between the second coordination bond and the quantum dot body is greater than the binding force between the first coordination bond and the quantum dot body, and the HOMO energy level of the second ligand is less than -6eV, and the LUMO energy level is -3.5eV to -1eV.

2. The quantum dot structure according to claim 1, characterized in that The electron mobility of the second ligand is 10 - 5 cm 2 / V·s~10 -3 cm 2 / V·s.

3. The quantum dot structure according to claim 1, characterized in that The first ligand includes a first coordination group, the first coordination group provides the first coordination bond, and the second ligand includes a second coordination group, the second coordination group provides the second coordination bond; Preferably, the first ligand group includes a combination of one or more of carboxyl, amino, polyamino or phosphorus oxygen groups; Preferably, the second coordination group includes a combination of one or more of thiol and polythiol.

4. The quantum dot structure according to claim 3, characterized in that The first ligand includes a combination of one or more of a straight-chain fatty acid ligand, a branched fatty acid ligand, a fatty amine ligand, and a phosphorus-oxygen ligand, wherein the straight-chain fatty acid ligand or the branched fatty acid ligand includes the carboxyl group, the fatty amine ligand includes the amino group or the polyamino group, and the phosphorus-oxygen ligand includes the phosphorus oxygen group.

5. The quantum dot structure according to claim 1, characterized in that The second ligand includes a non-coordinating group, and the non-coordinating group is connected to the quantum dot body through the second coordinating group; Preferably, the non-coordinating group includes one or more of a carbazolyl group, a phenyl group, an aniline group, a phenyl ether group, a phenylthio group, a thienyl group, a benzothienyl group, and a benzofuranyl group.

6. The quantum dot structure according to claim 5, characterized in that The second ligand has the following structural formula (I) or (II): Wherein, the R1 is the second coordination group, and R1 is selected from: -(CH2) n SH, n is any integer from 2 to 18; R2 and R3 are each independently selected from at least one of hydrogen, hydroxyl, C1-C36 alkyl which may be substituted or unsubstituted, C1-C36 cyano which may be substituted or unsubstituted, and C1-C36 phenyl which may be substituted or unsubstituted, wherein the substituent is F, Cl, Br, or I; R4, R5, R6, R7, and R8 are each independently selected from at least one of F, Cl, Br, I, CN, and OH; Preferably, the structural formula of the second ligand includes one or more combinations of the following:

7. A quantum dot light-emitting device, characterized in that: The invention comprises a substrate, a first electrode, a first functional layer, a quantum dot light-emitting layer, a second ligand layer, a second functional layer and a second electrode stacked in sequence on one side of the substrate; In which, the first electrode includes an anode, the first functional layer includes a hole injection layer and a hole transport layer stacked in sequence, the second electrode includes a cathode, the second ligand layer includes the second ligand, the second functional layer includes an electron transport layer, and the quantum dot light-emitting layer includes the quantum dot structure of any one of claims 1-7.

8. The quantum dot light-emitting device according to claim 7, characterized in that: The HOMO energy level of the second ligand is less than -6eV, and the LUMO energy level is -3.5eV to -1eV; Preferably, the electron mobility of the second ligand is 10-5cm 2 / V·s~10-3cm 2 / V·s; Preferably, the second ligand has the following structural formula (I) or (II): Wherein, the R1 is the second coordination group, and R1 is selected from: -(CH2) n SH, n is any integer from 2 to 18; R2 and R3 are each independently selected from at least one of hydrogen, hydroxyl, C1-C36 alkyl which may be substituted or unsubstituted, C1-C36 cyano which may be substituted or unsubstituted, and C1-C36 phenyl which may be substituted or unsubstituted, wherein the substituent is F, Cl, Br, or I; R4, R5, R6, R7, and R8 are each independently selected from at least one of F, Cl, Br, I, CN, and OH; Preferably, the structural formula of the second ligand includes one or more combinations of the following:

9. A method for preparing a quantum dot light-emitting layer comprising the quantum dot structure according to any one of claims 1 to 6, or a method for preparing the quantum dot light-emitting layer in the quantum dot light-emitting device according to claims 7 to 8, characterized in that: include: (1) treating the quantum dot body with the first ligand to obtain the quantum dot structure with the first ligand coordinated to any binding site on the surface; (2) forming the material obtained in step (1) into a thin film to form a quantum dot light-emitting layer in which any binding site on the surface is coordinated with the first ligand; (3) Using a second ligand treating agent containing the second ligand to treat the surface arbitrary binding sites obtained in step (2) to coordinate the quantum dot light-emitting layer of the first ligand away from the surface of the substrate, to form the quantum dot light-emitting layer and the second ligand layer.

10. The method for preparing a quantum dot light-emitting layer according to claim 9, characterized in that: The HOMO energy level of the second ligand treatment agent is lower than the HOMO energy level of the quantum dot light-emitting layer; Preferably, the LUMO energy level of the second ligand treatment agent is higher than the LUMO energy level of the quantum dot light-emitting layer; Preferably, the LUMO energy level of the second ligand treating agent is smaller than the LUMO energy level of the hole transport layer.

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